Glomerular Endothelial Fenestrae In Vivo Are Not Formed from Caveolae

Sörensson, Jenny; Fierlbeck, Wolfgang; Heider, Torsten; Schwarz, Karin; Park, David; Mündel, Peter; Lisanti, Michael P.; Ballermann, Barbara J.

doi:10.1097/01.asn.0000033277.32822.23

Cited by 70 publications

(64 citation statements)

References 29 publications

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“…[32][33][34] To understand the role of INF2 in maintaining nephrin-podocin complex trafficking, we investigated the interaction of INF2 with podocin and nephrin, as well as the lipid raft scaffolding protein caveolin-1. 35 As shown in Figure 4, A and B, in HEK 293T cells that overexpressed specific SD proteins, endogenous INF2 was co-immunoprecipitated with overexpressed hemagglutinin (HA)-podocin, but was immunoprecipitated by nephrin only in the presence of HA-podocin This finding indicates that podocin mediates an association of INF2 with nephrin. The interactions of endogenous INF2 with endogenous lipid raft components podocin and caveolin-1 were verified by co-immunoprecipitation in differentiated podocytes ( Figure 4C).…”

Section: Inf2 Directs Lipid Raft-mediated Lamellipodial Trafficking Omentioning

confidence: 84%

Inverted Formin 2 Regulates Actin Dynamics by Antagonizing Rho/Diaphanous-related Formin Signaling

Sun

Schlöndorff

Higgs

et al. 2013

Journal of the American Society of Nephrology

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Mutations in inverted formin 2 INF2 are a common cause of familial FSGS. INF2 interacts with diaphanousrelated formins (mDia) and antagonizes mDia-mediated actin polymerization in response to active Rho signaling, suggesting that dysregulation of these pathways may mediate the development of INF2-related FSGS. However, the precise mechanisms by which INF2 regulates actin-dependent podocyte behavior remain largely unknown. Here, we investigated the possible role of INF2 in both lamellipodia-associated actin dynamics and actin-dependent slit diaphragm (SD) protein trafficking by manipulating the expression of INF2 and the activity of Rho/mDia signaling in cultured podocytes. Activation of mDia in the absence of INF2 led to defective formation of lamellipodia and abnormal SD trafficking. Effects of mutations disrupting the INF2-mDia interaction suggested the specificity of the mDia-antagonizing effect of INF2 in maintaining the lamellipodium. Furthermore, we found that SD trafficking requires INF2 interaction with lipid raft components. In summary, INF2 regulates lamellipodial actin dynamics and the trafficking of slit diaphragm proteins by opposing Rho/mDia-mediated actin polymerization. Thus, in podocytes, INF2 appears to be an important modulator of actin-dependent behaviors that are under the control of Rho/ mDia signaling. Podocytes are terminally differentiated epithelial cells with interdigitating processes that wrap around and support the capillaries of the kidney's glomeruli. The terminal portions of these actin-rich extensions, known as foot processes (FPs), are bridged by cell-cell junctions called slit diaphragms (SD), a complex of proteins anchored at adjacent FPs. 1,2 FPs are polarized cytoplasmic processes with an apical-basal junction demarcated by the SD complex. 3 The SD protein complex participates in regulating the morphology and filter function of podocytes through crosstalk with actin remodeling pathways. 4,5 Ultrastructural studies have shown that the FPs contain a central actin bundle surrounded by a cortical actin network. This cortical actin is essential for maintaining the morphology and function of podocytes. 6 Through direct connections with the plasma membrane of FPs, cortical actin serves as a scaffold for SD proteins and their communication with actin filaments through signaling pathways and actin-binding proteins. 6,7 Actin reorganization and SD protein translocation accompany the foot process effacement and loss of the filtration barrier seen in proteinuric diseases. 8

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Section: Inf2 Directs Lipid Raft-mediated Lamellipodial Trafficking Omentioning

confidence: 84%

Inverted Formin 2 Regulates Actin Dynamics by Antagonizing Rho/Diaphanous-related Formin Signaling

Sun

Schlöndorff

Higgs

et al. 2013

Journal of the American Society of Nephrology

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“…It has also been suggested that VEGF-R1-Fyn/Yes complexes localize to caveolae fractions of endothelial cells (21), which might also be the case in podocytes. Of interest, caveolin-1, the principal protein that identifies caveolae in endothelial cells, is located in the foot processes of podocytes (39) and is therefore colocalized with nephrin. VEGF phosphorylation of its receptor in podocytes could induce the phosphorylation of the Src family of protein kinases, e.g., Fyn, and subsequently induce the phosphorylation of nephrin.…”

Section: Discussionmentioning

confidence: 99%

“…VEGF is also known to stimulate Fyn activa-tion in endothelial cells (29). Furthermore, VEGF receptors are known to colocalize with caveolin-1 in the plasma membrane of endothelial and mesangial cells (41), and caveolin-1 is coimmunoprecipitated with nephrin and CD2AP in podocytes (39). However, an association of VEGF receptors and nephrin has not been demonstrated.…”

mentioning

confidence: 99%

Vascular endothelial growth factor and nephrin interact and reduce apoptosis in human podocytes

Foster¹,

Saleem²,

Mathieson³

et al. 2005

American Journal of Physiology-Renal Physiology

112

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Vascular endothelial growth factor (VEGF) is anti-cytotoxic in podocytes. Moreover, it has been suggested that nephrin, a cell adhesion molecule of the podocyte slit diaphragm, can contribute to antiapoptotic mechanisms in these cells. We therefore investigated whether VEGF signals to reduce apoptosis and the role of nephrin in this survival mechanism. Flow cytometry showed that podocytes with nephrin mutations had a significantly greater proportion of apoptosis. Although VEGF reduced apoptosis in human conditionally immortalized podocytes [wild-type (WT)] by 18.1% of control ( P < 0.001), it was unable to do so in nephrin-deficient human conditionally immortalized podocytes. Moreover, Western blotting and immunodetection with an anti-nephrin antibody showed that the phosphorylation of nephrin, compared with serum-starved WTs, was significantly increased (ratio of 3.36 ± 1.2 to control, P < 0.05) by VEGF treatment and significantly reduced by treatment with a neutralizing VEGF monoclonal antibody (mAb) (ratio of 0.2 ± 0.09 to control, P < 0.05). The AKT signaling pathway has been implicated in nephrin-mediated inhibition of apoptosis in transfected cells, but the role of this pathway has not previously been shown in podocytes. Surprisingly, exogenous VEGF decreased AKT/PKB phosphorylation in normal podocytes but increased it in nephrin-deficient podocytes. We suggest therefore that both exogenous and endogenous (podocyte derived) VEGF can stimulate the phosphorylation of nephrin and through this action may prevent podocyte apoptosis. However, the involvement of AKT in this survival response in normal human podocytes is not clear.

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“…Because the ultrastructural lesions that occurred with albuminuria development in STZ-eNOS 2/2 mice occurred in podocytes, yet these cells are not known to express eNOS, 26 we hypothesized that the podocytopathy observed was a consequence of altered RAAS-dependent secreted factors. To determine whether podocyte morphology could be directly affected by circulating factors released in the setting of diabetes and eNOS deficiency, cultured podocytes were exposed to serum from the various study groups.…”

Section: Secreted Factors From Stz-enosmentioning

confidence: 99%

eNOS Deficiency Predisposes Podocytes to Injury in Diabetes

Yuen

Stead

Zhang

et al. 2012

Journal of the American Society of Nephrology

124

130

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Endothelial nitric oxide synthase (eNOS) deficiency may contribute to the pathogenesis of diabetic nephropathy in both experimental models and humans, but the underlying mechanism is not fully understood. Here, we studied two common sequelae of endothelial dysfunction in diabetes: glomerular capillary growth and effects on neighboring podocytes. Streptozotocin-induced diabetes increased glomerular capillary volume in both C57BL/6 and eNOS 2/2 mice. Inhibiting the vascular endothelial growth factor receptor attenuated albuminuria in diabetic C57BL/6 mice but not in diabetic eNOS 2/2 mice, even though it inhibited glomerular capillary enlargement in both. In eNOS 2/2 mice, an acute podocytopathy and heavy albuminuria occurred as early as 2 weeks after inducing diabetes, but treatment with either captopril or losartan prevented these effects. In vitro, serum derived from diabetic eNOS 2/2 mice augmented actin filament rearrangement in cultured podocytes. Furthermore, conditioned medium derived from eNOS 2/2 glomerular endothelial cells exposed to both high glucose and angiotensin II activated podocyte RhoA. Taken together, these results suggest that the combined effects of eNOS deficiency and hyperglycemia contribute to podocyte injury, highlighting the importance of communication between endothelial cells and podocytes in diabetes. Identifying mediators of this communication may lead to the future development of therapies targeting endothelial dysfunction in albuminuric individuals with diabetes.

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Glomerular Endothelial Fenestrae In Vivo Are Not Formed from Caveolae

Cited by 70 publications

References 29 publications

Inverted Formin 2 Regulates Actin Dynamics by Antagonizing Rho/Diaphanous-related Formin Signaling

Inverted Formin 2 Regulates Actin Dynamics by Antagonizing Rho/Diaphanous-related Formin Signaling

Vascular endothelial growth factor and nephrin interact and reduce apoptosis in human podocytes

eNOS Deficiency Predisposes Podocytes to Injury in Diabetes

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